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How Friendly Are Bio-Based Greases with Other Greases?

 

Royal 

Presented at NLGI's 79th Annual Meeting, June, 2012, Palm Beach, Florida, USA

Published in NLGI Spokesman Vol 77 No. 2 May/June 2013

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1.     Introduction

The applications of lubricants based on vegetable oils/animal fats were known to mankind since our ancient past and continued to be used until the 19th century when they were suddenly replaced by mineral oil, and to a lesser extent, by synthetic oil based lubricants and greases [1-2]. These mineral oil based and/or synthetic oil based greases have continued to dominate even today. The NLGI 2010 Grease Production Survey indicates over 2.3 billion lbs. of total worldwide grease volume were mineral oil based greases which dominated by about 93%, followed by synthetic and semi-synthetic oil based greases, or about 3% each. Biobased greases found their entry for the first time in this survey, though only about a 1% market share [3].

Lubricating grease based on oils from vegetable sources has been reported as early as the 1940's, however, their practical applications appear to have been reported in the 1960's [4, 5]. The usage of bio-based greases has been pretty spotty since then, until recently.

The main reasons for their limited applications appear to be their limited performance, high price and lack of support from environmental/ governmental agencies. More recently, growing environmental consciousness, drive for products based on renewable sources, legislative compliances, etc., once again revived bio-based greases. The further advancement in base oil chemistry and processes coupled with additive chemistry to improve the performance of these bio-based fluids has further provided support for their growth. Consequently, more and more lubricating greases based on different base oils viz., canola oil, rapeseed oil, soybean oil, sunflower oil, castor oil, synthetic esters, etc., have recently been reported from different parts of the world. These bio-based greases have increasingly found applications in various industries like agriculture, forestry, mining, water treatment/sewage treatment, off shore, railroad, automotive applications, etc. [6-10]. As the majority of lubricating greases presently being used are mineral oil based, it is likely that these vegetable oil based greases, possibly, are going to replace mineral oil based greases or, to a lesser extent, by synthetic oil based greases.

The compatibility of greases with one another is a very important property that plays a vital role in actual applications like centralized lubrication systems and the applications where complete cleaning or replacement of existing grease is very difficult. If two greases are not compatible with each other, it is likely that the mixed grease changes its physical or chemical property and may lead to the premature failure of bearing/equipment. Compatibility of greases also plays a crucial role while manufacturing, as complete cleaning of the manufacturing vessel/ kettle, filling and finishing line is extremely difficult. If two greases are not compatible, and one is produced over the other, it is possible the quality of fresh grease added later may be adversely affected. The incompatibility of lubricating greases is well known to the industry and compatibility studies are well documented and reported [11-12]. NLGI and others have published grease compatibility charts which indicate the compatibility of different types of thickeners [13]. Until very recently, these studies were limited to different types of thickener systems however nothing significant on the influence of base oil on the compatibility has been reported Influence of base oil on the compatibility appears to be relevant, considering the fact that finished lubricating greases consist of over 80% of base oil itself and does influence end use properties. These studies become more significant when considering the change over from a mineral oil based grease, to a bio-based grease as mineral oils primarily consist of hydrocarbons, whereas bio-based oils are triglycerides of long chain fatty acids. In view of this, compatibility studies of greases made in different base oils having the same type or different type of thickeners have been recently reported by this author [14]. However, these preliminary studies were limited to the greases having no additives and no effort was made to study the compatibility of fully formulated greases. Lou Honary et.al, has also recently reported compatibility studies on soy based greases [15], where it was reported that fully formulated soy based greases were found to be compatible with other greases. In our present study, efforts have been made to investigate the effect of canola oil based greases, both with and without additives, with other commercially available mineral and synthetic oil based greases. Some interesting results of these investigations have been covered in this paper.

2.     Experimental:

 

 The protocol for evaluating the compatibility of various greases, have been described in the ASTM D 6185-10 test method [16] and therefore the compatibility studies in this paper were carried out based on this test method. The ASTM-D 6185-10 test method delineates two stages of testing requirements. The first one is primary (mandatory) testing and the other one is secondary (non-mandatory) testing. As per method, binary mixtures in 10:90, 50:50 and 90:10 ratios are prepared by physical mixing. These mixtures along with neat greases are tested first for primary testing The vegetable oils used in these studies were commercially available technical grade canola oil. Properties of the canola oil are listed in Table 1.  Mineral base oils used for making these greases are either paraffinic and /or naphthenic oils. The thickeners selected for making vegetable oil based greases were of three types, namely lithium complex, aluminum complex and lithium-calcium mixed based. Other mineral oil based greases prepared for studying compatibility with vegetable oil based greases were lithium, lithium complex, aluminum complex, calcium sulfonate complex, and lithium-calcium mixed base greases and contain performance EP-AW, Anti-oxidant, rust inhibitors, tackifier/viscosity modifiers, etc. All the bio-based grease samples were prepared in a lab and the mineral or synthetic oil based greases used in these studies are commercial plant manufactured greases. All neat and mixtures were tested as per standard ASTM test methods. The storage stability of the samples was tested according to Federal Test Method 791C, Method 3467.1 at 120 ± 3°C (248 ± 3°F) for 24 ± 1 /4 h instead of 70 ± 1 /4 h. The reason for this deviation is that vegetable oils indicated faster deterioration at elevated temperatures for prolonged periods of time.

3.     Results and Discussion:

 

 NLGI defines incompatibility as: "two greases show incompatibility when a mixture of two products shows physical or service performance, which are markedly inferior to those of either of the greases before mixing. The properties or performance inferior to one of the products and superior to the other, may be due to simply mixing, and would not be considered as evidence of incompatibility." As per ASTM 6185-10 primary test protocol, the properties to be tested are mechanical stability (penetration after 100,000 strokes), dropping point and storage stability at high temperatures. Therefore, these properties have been tested for neat as well as binary mixtures. In addition to these, roll stability and weld load has also been tested for some mixtures, blend of group II and Group I paraffinic oil and does not contain any additive. The penetration test results have been shown in Figure 2 (b). Figure 2  (b) indicates that worked penetration after 10,000 strokes, and worked penetration after elevated temperature storage stability of blends, fall within penetration limits of neat Grease-1 and Grease-3. The dropping point of mixtures were found to be within the limits of the dropping point of Grease-1 and Grease-3 and thus considered compatible. The compatibility of Grease-1 was also studied with Grease-4 (prepared in 8 cSt polyalphaoliffins oil and no additives). Like Grease-3 worked penetration after 10,000 strokes, elevated temperature storage stability and drop points were found to be well within the limits of the two neat greases (Table 3).  Based on these test results, it may be inferred that bio-based aluminum complex grease (Grease-1), having no additives is compatible with other aluminum complex greases having no additives, and prepared in naphthenic oil (Grease-2), blend of group II and group I (Grease-3) and synthetic PAO oil (Grease-4). In order to study the influence of additives on the compatibility of bio-based aluminum complex grease, Grease-1 was studied with other aluminum complex greases having different performance additives. Grease-5 is prepared in naphthenic base oil and contains additives (Table 3).  Worked penetrations of Grease-1 and Grease-5 mixtures were found to be within penetration range of the two neat greases. However, worked penetration of the 50:50 mixture was found to be 340, 5 units higher than Grease-5 which is stability tests for blends, and the neat greases where roll stability tested after 2 hrs. for 50:50 blends, and were found to be off by 6 units. Whereas, the elevated temperature storage stability data fell within the limits of neat Grease-1 and Grease-6. Similarly, the dropping point of the mixtures fell within the dropping point of Grease-1 and Grease-6 (Table 3). This indicates the borderline compatibility of Grease-1 and Grease-6. On the other hand, compatibility data of Grease-1 with Grease-7 (Figure 3 (c)) indicate that Grease-1 is compatible with Grease-7. Grease-7 is an aluminum complex grease prepared in paraffinic oil (VG 150) and contains 2.0% antimony dialkyldithiocarbamate, 1% zinc dialkyldithiophosphate, 1% fatty acid derivative of 4, 5-dihydro-1 H imidazole and 5% blend of molybdenum disulphide and graphite.

Based on the above studies, it may be inferred that canola oil based aluminum complex grease having no additives (Grease-1) is found to be compatible with an aluminum complex greases prepared in mineral oil or synthetic oil and not having any additives. However, Grease-1 was found to be borderline compatible with two out of three aluminum complex greases having conventional performance additives.

3.2 Compatibility of Bio-Based Aluminum Complex Grease (No Additives) with Lithium Complex Greases:

The NLGI compatibility chart indicates that aluminum complex greases are compatible with lithium complex greases, therefore in order investigate the effect of biobased aluminum complex grease on the compatibility of lithium complex greases, this study was undertaken. Lithium complex greases selected for these studies meets NLGI GC-LB specification requirements except Grease-8, and do not have any additives. Though weld load is not included in the primary test protocol of the ASTM D 6185-10 test method, this test was considered worthwhile as these lithium complex greases are EP (extreme pressure) type greases, and the effect of mixing with bio-based grease may possibly have influenced this property. Grease-8 was prepared in naphthenic oil and does not contain any additive. Figure 4 (a) indicates that worked penetrations after 10,000, as well as 100,000 strokes, and elevated temperature storage stability data of mixtures fall within the limits of neat Grease-1 and neat Grease-8. On the other hand, the dropping points of Grease-1 and Grease-8 were 282°C and 267°C respectively, whereas the dropping point of 90:10, 50:50 and 10:90 blends are 260°C, 251 °C and 263°C, which are lower than the dropping point of either Grease-1 or Grease-8 (Table 3). This indicates that Grease-1 is not compatible with Grease-8 due to lower dropping points. Further, the compatibility of Grease-1 with Grease-9 was also studied (Figure 4 (b)), where Grease-9 is lithium complex grease prepared in a blend of naphthenicparaffinic oil (VG 220) and contains a 3.5% blend of antimony dialkyldithiocarbamate and zinc dialkyldithiophosphate, 1% fatty acid derivative of 4, 5-dihydro-1 H imidazole and 0.5% OCP polymer. Like Grease-8, mechanical stability (both penetration after 10,000 and 100,000 strokes), elevated temperature storage stability and weld loads of Grease-1 and Grease-9 mixtures and fall with the limits of neat Grease-1 and Grease-9. However, the dropping point of the mixtures were found to be lower than the dropping point of either greases (Table 3) and therefore inferred incompatible. A similar trend has been observed between Grease-1 and Grease-10 (Figure 4 (c)) where Grease-10 is lithium complex prepared in heavier naphthenic Oil (VG 460) and contains more amounts of additives than Grease-9. A similar observation has been found when the compatibility of Grease-1 was studied with Grease-11 (Table 3), where Grease-11 is a lithium complex grease prepared in synthetic oil (PAO 8) and contain a 3.0% blend of sulfurized isobutylene and zinc dialkyldithiophosphate, 1% barium sulfonate, 1% alkylated diphenylamine. Though different penetration values of the blend fall within the values of neat greases (Figure 4 (d)), the dropping point of the blends fell considerably (Table-3) as compared to either Grease-1 or Grease-11, indicating the incompatibility. These blends were also tested for weld load and the results (Table-3) did not indicate any adverse effect as a result of mixing.

3.3 Compatibility of Bio-Based Aluminum Complex Grease (With Additives) with Other Additive Containing Greases:

Grease-12 is aluminum complex grease prepared in canola oil and contains a 4% blend of calcium carbonate, graphite, 3% blends of ashless polysulfide and sulfur-phosphorous-nitrogen containing EP-AW additive, and 0.5% bio-based tackifier. Compatibility of Grease-12 was first tested with Grease-5, which was an aluminum complex grease prepared in naphthenic oil (VG 150) and contains performance additives, as indicated in Table 2. Figure 5 (a) and Table-3 indicates that worked penetration after 10,000 strokes, elevated temperature storage stability, dropping point and weld load of 90:10, 50:50 and 10:90 mixtures fell within the limits of neat Grease-12 and Grease-5. Which indicates that bio-based aluminum complex grease containing additives (Grease-12) was found to be compatible with mineral oil based aluminum complex grease containing additives (Grease-5). To further investigate the compatibility of additized bio-based grease (Grease-12) with more greases, compatibility studies were conducted with different additized lithium complex greases. Compatibility data of Grease-12 with Grease-9 are tabulated in Table 3 and also depicted in Figure 5 (b) where Grease-9 is a lithium complex prepared in a blend of Naphthenic-Paraffinic oil (VG 220) and contains

additives (Table 2). Figure 5 (b) indicates that worked penetration after 10,000 and 100,000 strokes, elevated temperature storage stability and weld load of the mixtures fell within the limits of neat Grease-12 and Grease-9. On the other hand, the dropping point of the mixtures was found to be less than either of the neat greases. Though grease mixtures pass the test criteria in other tests, lower dropping points of the mixtures indicate that Grease-9 and Grease-12 are not compatible. Similarly, compatibility data of Grease-12 with Grease-10 where Grease-10 is lithium complex grease prepared in a higher base oil viscosity oil (VG 460) and contains more additives than Grease-9 Figure 5  (c), indicate that the mixtures of Grease-10 and Grease-12 meet the penetration, even weld load but do not meet the dropping point requirements (Table-3) and thus deemed incompatible. To further validate this observation, compatibility of Grease-12 was tested with a synthetic oil based lithium complex grease (Grease-11) containing additives as described in Table-2.  Like Grease-9 and Grease-10, mixtures of Grease-12 with Grease-11 exhibited lower dropping point (Table-3)  though comparative penetrations appear to be fine (Figure 5 (b)) thus concluded as incompatible. These studies indicate that additized bio-based aluminum complex grease was found to be compatible with additized mineral oil based aluminum complex grease, but incompatible with additized mineral oil, and also synthetic oil, based lithium complex greases.

3.4 Compatibility of Bio-Based Lithium Complex Greases with Other Greases:

Another class of bio-based grease studies, is lithium complex greases. Grease-13 is a lithium complex grease prepared in canola oil and does not contain any additives. Its compatibility was first studied with mineral oil based lithium complex grease that does not contain any additives (Grease-8) and the test result is depicted in Figure 6 (a) and also in Table-4. Test data indicate that worked penetration after 100,000 strokes, elevated temperature storage stability and dropping point of the mixtures, fall within the limits of neat Grease-13 and Grease-8, and are therefore considered compatible. The compatibility of Grease-13 was further studied with lithium complex grease (Grease-9), that contains additives as described in Table 2. Figure 6 (b)) and Table 4, data analysis would confirm that Grease-13 and Grease-9 are compatible. Grease-13's compatibility was also studied with mineral oil based, additized aluminum complex grease (Grease-5). Worked penetration after 100,000 strokes and elevated temperature storage stability data of the mixtures appears to be well within the limits of neat greases (Figure 6 (c)), whereas the dropping point (Table 4) of the mixtures (especially 50:50 blend) was found to be much lower than either of the greases, indicating incompatibility. Compatibility of Grease-13 was also evaluated with calcium sulfonate complex grease (Grease-14) with additives. Mechanical stability and elevated temperature storage stability data of the mixtures (Figure 6 (d)) were found to be within the limits. However, the dropping point (Table-4) of all the blends (especially 50:50 blend) was found to be much lower than neat greases, and thus incompatible. It is therefore inferred that bio-based lithium complex grease without any additives, was found to be compatible with both with/without additives mineral oil based lithium complex greases, but incompatible with additized mineral oil based aluminum complex and calcium sulfonate complex greases. To further validate this observation, compatibility of bio-based lithium complex grease (Grease-15), prepared in canola oil, having a 3.5% blend of Ashless polysulfide and sulfur-phosphorous-nitrogen containing EP-AW additive, and 2%  bio-based tackifier, was studied with other greases. Figure 7 (a) and Table-4  indicate that  Grease-15 with Grease-8, which is a mineral oil based lithium  complex grease  having no additives, are compatible. On the other  hand, compatibility test data of Grease-15 with Grease-9 (mineral oil based lithium complex  grease containing additives), indicate  that 100,000  strokes worked  penetration, elevated temperature storage stability (Figure  7 (b))  and weld load, fall within  the limits of  neat greases, but the dropping  point of the 50:50 mixture was found  to be much less than any individual neat grease, and  therefore incompatible. Compatibility data (Figure 7 (c)  and Table-4)  of Grease-15 with additized  mineral oil based  aluminum complex  grease (Grease-5), indicate that, though the 100,000  strokes worked  penetration, elevated temperature storage  stability and weld  load fall well with the limits of  individual neat greases,  the dropping point  of all the  mixtures were found to be lower  than that of either of the neat  greases. The similar trend was observed when  compatibility of Grease-15 was tested with  additized calcium sulfonate complex grease (Grease-14)  and test data are depicted in Figure  7 (d) and Table-4.  It is concluded  that bio-based lithium  complex grease having  EP-AW additives,  was found to  be compatible  with mineral oil  based lithium complex  grease (no-additives), but incompatible with mineral oilbased additized  lithium complex, aluminum complex and calcium sulfonate complex greases.

3.5 Compatibility of Bio-Based Lithium-Calcium Greases with Other Greases:

Another  type of bio-based grease considered for  these studies, are additized bio-based lithium-calcium grease (Grease-16). Grease-16  is lithium-calcium  grease prepared in  canola oil  and contains a 3.0% blend of Ashless polysulfide, sulfur-phosphorous-nitrogen  containing  EP-AW additive, 1% rust  inhibitor and 2.5%bio-based tackifier.  Compatibility of Grease-16 was first studied with mineral oil  based additized  lithium-calcium grease  (Grease-17). The test data (Table 4 and Figure  8 (a)) indicate  that the  values of  the test results of all the mixtures fall within the  limits of Grease-16 and Grease-17 thus  considered compatible. Grease-16  was further tested with Grease-9, which is a  mineral oil additized lithium complex grease. Worked penetration after 100,000 strokes, elevated temperature storage stability (Figure 8  (b)), dropping point and weld load data (Table-4)  of the mixtures tested, indicate that the two greases are compatible. However, when Grease-16 was tested with Grease-5, which is an additized mineral oil based aluminum complex grease, it exhibited incompatibility in terms of mechanical stability, elevated temperature storage stability and dropping point (especially 50:50 blend) (Figure 8  (c) and Table 4).  Compatibility of Grease-16 was also tested with Grease-14, a mineral oil based additized calcium sulfonate grease. The test data of the mixtures (Figure 8  (d) and Table 4)  indicate that the worked penetration, after 100,000 strokes, elevated temperature storage stability and dropping points of all the mixtures, and fell within the limits of neat Grease-16 and Grease-14. Based on the test data as described in Table-4,  it can be concluded that biobased lithium-calcium grease, containing performance additives, is compatible with mineral oil based additized lithium-calcium, lithium complex and calcium sulfonate complex greases, but incompatible with mineral oil based, additized aluminum complex grease.

4.0 Conclusions:

 The compatibility of canola oil based aluminum complex, lithium complex and lithium-calcium greases, either with or without additives, was studied with different aluminum complex, calcium sulfonate complex, and lithium complex greases, prepared in different base oils and containing different additives. These studies are limited to canola oil based greases, and no attempts have so far been made to study compatibility of these greases prepared in other bio-fluids. It has been interesting to note that canola oil based aluminum complex grease, without any additives, was found to be compatible with mineral oil or synthetic oil based aluminum complex greases, having no additives, but found to be borderline compatible with two out of three aluminum complex greases, having additives and prepared in mineral/ synthetic oils. However, the same grease was found to be incompatible with mineral/synthetic oil based lithium complex greases, having performance additives. Additionally, additized canola oil based aluminum complex grease, was found to compatible with additized, mineral oil based aluminum complex grease, but incompatible with additized lithium complex greases. These compatibility studies were further extended to canola oil based lithium complex grease. Test results indicate that canola oil based lithium complex grease, without any additives was found to be compatible with mineral oil based lithium complex grease, having no additives and also with additives; however was found to be incompatible with additized, mineral oil based aluminum and calcium sulfonate greases. When the compatibility of additized canola oil base lithium complex grease, was studied with mineral oil based lithium complex grease, without any additives, and was found compatible. However, the same grease was found to be incompatible with additized lithium complex, aluminum complex and calcium sulfonate complex greases. Interestingly, canola oil based lithium-calcium grease, containing performance additives, was found to be compatible with additized lithium complex and calcium sulfonate complex greases, although incompatible with additized aluminum complex greases. It appears from these studies that the properties, especially dropping points, of the blends of two greases are considerably influenced and dependent on the type of thickener and amount of additives present in either finished grease; however there was no significant impact on penetrations. These studies could not establish any generalized trend, and therefore, more elaborate studies may be necessary to investigate further.

Acknowledgement:

 The authors wish to acknowledge grease plant personnel, especially Monte Walton, for the assistance in arranging the samples and other inputs for these studies. Authors are also thankful to the management of Royal Mfg. Co. LP for all necessary assistance in carrying out this work and granting permission to report such work.

References:

 [1] Boner, C. J., "Manufacturing and Applications of Lubricating Greases"  Reinhold Publishing Corp., 430 Park Ave. NY, 1954, pp. 136-138.

[2] Polishuk, A.T., "A Brief History of Lubricating Greases"  Llewellyn & McKane Inc. PA, 1998, pp. 35-72

[3] NLGI, "Grease Production Survey Report" Kansas City, Missouri, 2010.

[4] Nicholaichuk, M. P., "Field Testing and Commercial Experience with Lithium Rapeseed Grease" NLGI

Spokesman,  Vol. 35(12), 1962, pp. 153-154.

[5] McNichol, M. A., "A Co-op First Rapeseed Oil Grease" NLGI Spokesman,  Vol. 24(10), 1961, pp. 408-409.

[6] Honary, L., "Performance Characteristics of Soybean Based Greases Thickened with Clay, Aluminum Complex and Lithium" NLGI Spokesman,  Vol. 65(8), 2001, pp. 18-27.

[7] Kumar, A., et al., "Eco-Friendly Titanium Complex Grease" NLGI Spokesman,  Vol. 61(8), 1997, pp. 22-28.

[8] Kieke, M. D. and Klein, R. J, "Earth Friendly Vegetable Oil Based Greases Thickened with Organophilic Clay" NLGI Spokesman,  Vol. 67(9), 2003, pp. 14-16.

[9] Hocine, F., Medrano, A. and Cisler, B., "Biodegradable Open Gear Lubricant" NLGI Spokesman,  Vol. 67(12) 2004, pp. 121-135

[10] Stempfel, E. M. and Baumann, M., "Environmentally Acceptable Lubricants in Railway Applications"

Eurogrease,  September/October, 2004, pp. 19-34.

[11] Myers, E. H., "Incompatibility of Greases" NLGI Spokesman,  Vol. 47(4), 1983, pp. 24-32.

[1 2]  Mistry, A., "Grease Compatibility Revisited" NLGI Spokesman,  Vol. 64(10), 2001, pp. 24-30.

[13] Boner, C. J., "Modern Lubricating Greases"  Scientific Publishing (G.B.) Ltd, Shropshire, England, 1976, pp. 2.20.

[14] Kumar, A., et al., "Compatibility of Vegetable Oil Based Greases with Different Mineral Oil Based Greases" Journal of ASTM International, Vol. 8. No. 9, 2011.

[15] Honary, L., "A Study of Compatibility of Fully Formulated Bio-based and Conventional Greases" presented at 78th NLGI Annual Meeting, Palm Desert California, June 2011.

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[16] ASTM Standard D6185-10, "Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases" ASTM Annual Book of Standards,  2010, Vol. 05.03 ASTM  International, West Conshohocken, PA.

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